Carburetors

ABSTRACT

A carburetor of the constant depression type having a butterfly throttle valve is provided with an auxiliary passage for supplying air directly to the induction passage downstream of the throttle valve when the said throttle valve is in the idling position, opening of the throttle valve beyond the idling position causing the air supply through the auxiliary passage to a position downstream of the throttle valve to cease either due to the edge of the throttle valve moving across the auxiliary passage opening or to the said auxiliary passage being closed.

O I United States Patent 1 1 a 1 1 3,779,530 Lawrence Dec. 18, 1973 CARBURETORS 3,198,497 8/1965 Mennesson 2151/50 A [75] Inventor: Geoffrey Lloyd Lawrence,

Stanmore, England 3,295,839 1/1967 Mitchell 261/56 Assignee: The Zenith Carburetter p y 3,409,277 1 1/1968 RCISC 261/51 Limited, stanmore, Middlesex 3,455,260 7/1969 Mennesson 261/44 R England E T M Primary xaminer im R. iles [22] F'led: 1971 Attorney-Stevens, Davis, Miller & Mosher [21] Appl. No.: 127,206

[57] ABSTRACT [30] Forelg Apphcaum? P nomy Data A carburetor of the constant depression type having a Mar. 31, 1970 Great Brltam 15,079/70 butterfly throttle valve is provided with an auxiliary Y passage for supplying air directly to the induction pas- [22] l:J.S.CCII. 261/44 R, 261/56 Sage downstream of the throttle valve when the Said I throttle valve is in the gp p g of the [5 1 d of 261/44 50 A throttle valve beyond the idling position causing the air supply through the auxiliary passage to a position [5 6] References C'ted downstream of the throttle valve to cease either due to UNITED STATES PATENTS the edge of the throttle valve moving across the auxili- 1,722,934 7/1929 Medley 261/44 R ary passage opening or to the said auxiliary passage 2,827,269 3/1958 Kittler 261/56 being closed. 2,996,051 8/1961 Mick..... 261/50 A r 3,147,320 9/1964 Tubb 261/44 R 11 Claims, 6 Drawing Figures I I l I 1 F 2 i E 45 1 2.9 1\ a -24 44 33 2 x 5 2a 37 l 19 1,

v 3.779.530 [mama PATFNTED sum 20F 3 CARBURETORS This invention relates to carburetors for internal combustion engines, and, more specifically, to carburetors of the so-called constant depression type, in which there is provided in the induction passage of the carburetor, upstream of the throttle valve, an air valve which is controlled automatically in response to any tendency for the depression in the part of the induction passage, between the throttle valve and the air valve, which part is hereinafter called the mixing chamber, to change, so as to maintain the depression in the said mixing chamber substantially constant.

Fuel is supplied to the induction passage of such carburetors through anorifice leading into a throat the area of which is defined by the position of the air valve, the area of the orifice itself being varied by movement of a profiled needle extending through the said orifice and moving to increase the said area as the throat area is increased by movement of the air valve.

It has been found with such carburetors that it is a distinct advantage to be able to modify the fuel/air mixture metered for idling purposes to achieve close control of the toxic, CO content of the exhaust gases emitted during the idling mode. Further it is required to enable this adjustment tobe made without interfering with the metering characteristics established over the rest of the carburetor flow range.

To achieve this tuning facility it has been proposed to supply additional air directly to the induction manifold passage downstream of the carburetor throttle valve in some variable proportion with the effect that the position of the air valve and profiled needle is al tered for a given air flow to the engine thus altering the effective size of the main metering orifice.

According to a previous proposal, theadditional air was supplied to the mixing chamber, but the supply of additional air to the mixing chamber has been found to affect adversely both the quality of idling and the response of the carburetor to throttle movement in th range adjacent to the idling position.

It is an object of the present invention to provide an extra air supply arrangement which avoids or minimizes these disadvantages.

According to the present invention there is provided a carburetor of the constant depression type as herein defined and having a butterfly type throttle valve, wherein a further passage provided for supplying air directly 'to the induction passage at a position downstream of the throttle valve when the said throttle valve is in the idling position is so controlled by operation of the throttle valve that the supply of air through said further passage to the induction passage downstream of the throttle valve ceases when the said throttle valve has passed through a small range of movement in the opening direction from said idling position.

In one arrangement according to the invention, said further passage opens into the said induction passage at a position adjacent the edge of the throttle valve which moves away from the mixing chamber as the said throttle valve moves from its idling position, the said position of the passage opening being such that, when the throttle valve is in the idling position the said passage opening is on the downstream side of the throttle valve, the edge of the throttle valve passing across the said opening during a small range of movement from said idling position.

Preferably, the edge of the throttle valve is transferred from a position upstream of the passage opening to a position downstream thereof during an angular movement of the throttle valve such that the change in total air flow through the carburetor does not exceed one pound per minute.

The passage opening may be a circumferentially extending slot or a circumferentially extending row of holes so that, for a given area of the passage opening, the movement of the throttle valve edge necessary for said-edge to pass across the passage opening is relatively small.

Preferably, the slot or series of holes has a length such that it subtends an angle of not more than 6 at the center of the induction passage.

In another arrangement according to the invention, said further passage is controlled by a normally open valve closed by operation of the throttle valve to move it from its idling position.

The normally open valve may be coupled mechanically to linkage means for operating the throttle valve or may be closed by a solenoid energized by operation of the throttle valve to move it from the idling position.

- The normally open valve may be a rotary valve or a needle valve. I

Adjustable flow controlling means may be provided in said further passage, and said means may comprise a fixed flow restricting device and a variable flow restricting device arranged in parallel.

Some embodiments of the invention will now be described, by way of example, with'reference to the accompanying drawings, in which:

FIG. 1 is a partial longitudinal section of one form of carburetor embodying the invention;

FIG. 2 is a section on the line 2 2 of FIG. 1;

FIG. 3 is a section similar to FIG. 2 but showing a modification;

FIG. 4 is a partial longitudinal section, similar to FIG. 1, showing another embodiment of the invention;

FIG. 5 shows a detail modification of the embodiment shown in FIG. 4; and I FIG. 6 is a partial longitudinal section, similar to FIG.

. 1, showing another embodiment of the invention.

shown at 10, the induction passage of the carburetor,

which is shown at 11, having its inlet end at 12 and its outlet end, which is adapted to be connected through an inlet manifold (not shown) to the inlet ports of an internal combustion engine, at 13.

A butterfly type throttle valve 14 mounted in the in. duction passage 11 adjacent-its outlet end 13 is carried by a pivot shaft 15 arranged to be rotated by an operator through a mechanical linkage (not shown) to open and close the said throttle valve.

Intermediate the ends of the induction passage 11 there is provided a bridge 16 and an air valve slide 17 movable transversely across the induction passage 11. The air valve slide 17 co-operates with the bridge 16 to provide a variable throat at 18, the slide 17 being controlled in the usual manner by differential air pressure acting, in a housing (not shown) on opposite sides of a piston or diaphragm connected to the slide, in such a way that depression in the part of the induction passage between the air valve slide 17 and the throttle valve 14,

hereinafter called the mixing chamber 19, tends tocause movement of the slide away from the bridge and increase the area of the throat thereby maintaining the depression in the said mixing chamber 19 substantially constant.

A fuel supply orifice 21 opens into the bridge surface and is connected to a float chamber (not shown) containing fuel which is maintained at a constant level by a float-controlled valve, and a profiled needle 22, carried by the air valve slide 17, varies the effective area of the orifice 21 according to the position of the air valve.

The carburetor, as so far described, is conventional in construction and no further description of the parts referred to, or their operation, is deemed necessary.

A longitudinal passage 23 formed in the carburetor body 10, and closed by a plug 24 at its end adjacent the outlet end 13 of the induction passage, is connected at 25 to the induction passage 11 at a position such that when the throttle valve is in the idling position, as shown in FIG. 1, the connection is on the downstream side of the edge of the throttle valve 14 at the position, on a diameter of the throttle valve normal to its pivotal axis, where the said. throttle valve moves away from the air valve during its opening movement, so that a very small opening movement of the throttle valve causes its edge to move across the connection and bring the latter to the upstream side of the said throttle valve. The connection at 25 may be a circumferentially extending slot 26 as shown in FIG. 2, or a circumferential row of holes 27 as shown in FIG. 3, the slot or row of holes preferably subtending an angle of not more than 6 at the axis of the induction passage.

The longitudinal passage 23, at its end remote from the plug 24, meets a transverse passage 28 opening into a flat external surface 29 on the body into which also opens a passage 31 leading from the induction passage upstream of the air valve, and a flow restricting unit 32 is secured against the said flat external surface 29. A first passage 33 in the unit 32 connects with the passage 31, a second passage 34 in the unit 32, parallel to the passage 33, is closed at one end and connected at the other end by a passage 35 to the passage 33, and a further passage 36 connecting the passages 33 and 34 is connected intermediate its ends by a passage 37 to the passage 28.

A screw plug 38 mounted in a screw-threaded bore aligned with the passage 35 has a tapered end 39 seating in the passage 35 and is formed with intersecting bores 41, 42 providing a fixed flow restriction between the passages 33 and 34, and a second screw plug 43, mounted in a screw-threaded bore 44 aligned with the passage 36, has tapered portions 45 and 46 cooperating respectively with the parts of the passage 36 on opposite sides of the passage 37 to provide a variable restriction of flow between the passages 34 and 37. Thus the actual rate of flow of air through the passages 31, 23 can be approximately determined by selecting the area of the passages 41, 42 in the plug 38, and can be slightly varied in either the increasing or the decreasing senses by moving the plug 43 in or out.

In the arrangement shown in FIG. 4 of the drawings, the passage 23, instead of being a passage open at all times to the induction passage and traversed by the edge of the throttle valve 14 as the latter opens, has its opening to the induction passage spaced some distance downstream of the throttle valve, at 44a. A rotary valve plug 45a, having an L-shaped passage 46a therein, is attached to an arm 47 connected by a link 48 to a throt' tle valve operating arm 49 connected to a throttle control linkage (not shown) the arrangement being such that, when the throttle valve 14 is in the idling position, as shown, the passage 46a in the valve plug connects the passage 23 to the opening 44a, but a small opening movement of the throttle valve rotates the plug a to bring the passage 46a out of register with the passage 23 and opening 44a, thus shutting off the supply of air to the induction passage through the passage 23.

FIG. 5 shows an arrangement similar to that of FIG. 4, but in which the valve plug 45a is formed with a slot 51 instead of a passage 46a.

In the arrangement shown in FIG. 6 of the drawings, the passage 23 leads into a passage 52 opening into the induction passage 11 downstream of the throttle valve 14, the passage 52 being formed with a seating 53 for a needle valve 54 acted on by a solenoid 55 which, when energized, causes the needle valve to engage the seat. A normally open electric switch 56 is operated by an arm 57 fixed to the throttle valve spindle 15 so as to be closed when the throttle valve is moved slightly from the idling position, completing a circuit through the solenoid 55 and a battery 58 to energize the solenoid and so seat the needle valve 54.

Apart from the provision of the valves to close the connection between the passages 23 and the induction passages 11 the arrangements shown in FIGS. 4, 5 and 6 are substantially identical with that shown in FIG. 1.

Since, in all the embodiments of the invention described, the influence of the extra air supply is restricted to the idling condition and the condition close to idling, the said extra air supply does not interfere with the main metering characteristics of the carburetor.

The plug 43 of the flow restricting unit, or a further flow restricting device in the extra air supply passage, may be controlled by an aneroid capsule or other altitude sensing device to provide automatic fuel/air mixture compensation for changes of altitude at idling speeds.

The provision of an extra air supply passage according to the invention may obviate the need for other adjustments to control idling, such as adjustments of the relative positions of the fuel orifice and profiled needle for a given position of the air valve.

The air flow in the extra air supply passage may be used to provide a signal to operate a pneumatic ignition retarding capsule of known type.

I claim:

1. A carburetor comprising a body defining a first induction passage having an upstream end and a downstream end, a throttle valve of the pivoted flat type, including means for pivoting the same in said induction passage, said throttle valve having an idling position in which it is substantially closed, an air valve in said induction passage, said air valve cooperating with a wall of said induction passage to define a throat between said throttle valve and the upstream end of said induction passage, said throttle valve and said air valve defining between them a mixing chamber in said induction passage, means for supplying fuel to said throat, a second passage connected to said induction passage, said second passage being connected, at one end, only to the upstream end of said induction passage and upstream of said air valve and, at the other end, on the downstream side of said throttle valve when said throttle valve is in the idling position so that suction in said induction passage, when the throttle valve is in the idling position, creates air flow through said second passage, means including at least a part of said throttle valve responsive to the initial opening of said throttle valve from the idling position for eliminating the air flow creating suction in said second passage, and an adjustable flow controlling means provided in said second passage for controlling the flow of air, said adjustable flow controlling means including a fixed flow restricting device and a first variable flow restricting device in series with one another and in parallel with a second variable flow restricting device.

2. A carburetor according to claim 1 wherein the edge of said throttle valve is transferred from a position upstream of the other end of said second passage to a position downstream thereof during an angular movement of said throttle valve such that the change in total air flow through the carburetor does not exceed one pound per minute.

3. A carburetor according to claim 1 wherein the passage opening at said other end comprises a circumferentially extending slot.

4. A carburetor according to claim 1 wherein the passage opening at said other end comprises a circumferentially extending row of holes.

5. A carburetor according to claim 1 wherein said other end comprises an opening having a length such that it subtends an angle of not more than 6 at the center of the induction passage.

6. A carburetor as claimed in claim 1 in which said second passage opens into said induction passage at a position on a diameter of said throttle valve normal to the axis of said throttle valve where the edgeof said throttle valve moves, as said valve opens, towards the downstream end of said induction passage, and in which said second passage is open to said induction passage at a position which is immediately downstream of said throttle valve edge when said throttle valve is in the idling position, said latter position comprising said eliminating means.

7. A carburetor as claimed in claim 1 in which said eliminating means comprises a shut-off valve provided in said second passage, operating means for opening and closing said shut-off valve, a control device connected to said throttle valve and means linking said throttle valve control device and said operating means, said control device causing said operating means to open said shut-off valve when said throttle valve is in the idling position and to close said shut-off valve during initial opening of said throttle valve from the idling position.

8. A carburetor according to claim 7 wherein said control device includes a throttle valve operating arm and said shut-off valve is coupled mechanically through said operating and linking means to said operating arm.

9. A carburetor according to claim 8, wherein said shut off valve is a rotary valve.

10. A carburetor according to claim 7 wherein said operating means comprises a solenoid energized by movement of said throttle valve and said shut-off valve is electrically connected through said solenoid to said control device.

11. A carburetor according to claim 10, wherein said shut off valve is a needle valve. 

1. A carburetor comprising a body defining a first induction passage having an upstream end and a downstream end, a throttle valve of the pivoted flat type, including means for pivoting the same in said induction passage, said throttle valve having an idling position in which it is substantially closed, an air valve in said induction passage, said air valve cooperating with a wall of said induction passage to define a throat between said throttle valve and the upstream end of said induction passage, said throttle valve and said air valve defining between them a mixing chamber in said induction passage, means for supplying fuel to said throat, a second passage connected to said induction passage, said second passage being connected, at one end, only to the upstream end of said induction passage and upstream of said air valve and, at the other end, on the downstream side of said throttle valve when said throttle valve is in the idling position so that suction in said induction passage, when the throttle valve is in the idling position, creates air flow through said second passage, means including at least a part of said throttle valve responsive to the initial opening of said throttle valve from the idling position for eliminating the air flow creating suction in said second passage, and an adjustable flow controlling means provided in said second passage for controlling the flow of air, said adjustable flow controlling means including a fixed flow restricting device and a first variable flow restricting device in series with one another and in parallel with a second variable flow restricting device.
 2. A carburetor according to claim 1 wherein the edge of said throttle valve is transferred from a position upstream of the other end of said second passage to a position downstream thereof during an angular movement of said throttle valve such that the change in total air flow through the carburetor does not exceed one pound per minute.
 3. A carburetor according to claim 1 wherein the passage opening at said other end comprises a circumferentially extending slot.
 4. A carburetor according to claim 1 wherein the passage opening at said other end comprises a circumferentially extending row of holes.
 5. A carburetor according to claim 1 wherein said other end comprises an opening having a length such that it subtends an angle of not more than 6* at the center of the induction passage.
 6. A carburetor as claimed in claim 1 in which said second passage opens into said induction passage at a position on a diameter of said throttle valve normal to the axis of said throttle valve where the edge of said throttle valve moves, as said valve opens, towards the downstream end of said induction passage, and in which said second passage is open to said induction passage at a position which is immediately downstream of said throttle valve edge when said throttle valve is in the idling position, said latter position comprising said eliminating means.
 7. A carburetor as claimed in claim 1 in which said eliminating means comprises a shut-off valve provided in said second passage, operating means for opening and closing said shut-off valve, a control device connected to said throttle valve and means linking said throttle valve control device and said operating means, said control device causing said operating means to open said shut-off valve when said throttle valve is in the idling position and to close said shut-off valve during initial opening of said throttle valve from the idling position.
 8. A carburetor according to claim 7 wherein said control device includes a throttle valve operating arm and said shut-off valve is coupled mechanically through said operating and linking means to said operating arm.
 9. A carburetor according to claim 8, wherein said shut off valve is a rotary valve.
 10. A carburetor according to claim 7 wherein said operating means comprises a solenoid energized by movement of said throttle valve and said shut-off valve is electrically connected through said solenoid to said control device.
 11. A carburetor according to claim 10, wherein said shut off valve is a needle valve. 